MORGANTOWN, W.Va. (AP) -- Legislators have waited 31/2 years and spent more than $220,000 to learn whether coal slurry pumped into abandoned underground mines is dangerous to people who live nearby. The answer? No one knows.

A new 418-page report by researchers at West Virginia University concludes that while the wastewater from cleaning coal could potentially affect water supplies, wells and public health, there's no proof it has or will.

"No public health problem, attributable only to coal slurry, can be documented from available data,'' the report says.

But principal researcher Alan Ducatman and his team caution that they were forced to work with vast "data gaps'' and an inadequate understanding of how underground injection works in reality rather than theory.

"The absence of sufficient data implies a need to learn,'' their report says. "It does not necessarily imply the absence or presence of a problem or a means to do assessments in the absence of data.''

One legislator argues that if the practice cannot be deemed safe, it should be stopped.

"We shouldn't be playing Russian roulette with public health,'' said state Sen. Jeff Kessler, D-Marshall.

Slurry is created when coal is washed to help it burn more efficiently. For decades, coal companies in Appalachia have injected slurry into worked-out underground mines as a cheap alternative to building dams or filtration and drying systems. The report says 70 million to 90 million gallons of slurry is created nationwide each year.

In theory, solids settle to the bottom of pools inside sealed mine voids, and all the waste stays put, with little risk to groundwater below.

The industry defends the practice as safe. But critics say the earth continues to shift and crack long after mining has ended, whether through natural settling or activity such as nearby blasting. They say that lets slurry migrate, sometimes into drinking water supplies. Hundreds of southern West Virginia residents are now suing coal companies, claiming slurry poisoned their wells and made them sick.

WVU's report says federal documents and other literature provide reason to believe injection "does not always work as intended'' and can contaminate ground and surface water.

But there is virtually no useful monitoring data from the 12 active injection sites in West Virginia or dozens of others that were used for decades, the report says, and therefore no practical way to determine whether the slurry underground contains anything other than the 237 legally permissible chemicals.

A new 418-page report by researchers at West Virginia University concludes that while the wastewater from cleaning coal could potentially affect water supplies, wells and public health, there's no proof it has or will.

"No public health problem, attributable only to coal slurry, can be documented from available data,'' the report says.

But principal researcher Alan Ducatman and his team caution that they were forced to work with vast "data gaps'' and an inadequate understanding of how underground injection works in reality rather than theory.

"The absence of sufficient data implies a need to learn,'' their report says. "It does not necessarily imply the absence or presence of a problem or a means to do assessments in the absence of data.''

One legislator argues that if the practice cannot be deemed safe, it should be stopped.

"We shouldn't be playing Russian roulette with public health,'' said state Sen. Jeff Kessler, D-Marshall.

Slurry is created when coal is washed to help it burn more efficiently. For decades, coal companies in Appalachia have injected slurry into worked-out underground mines as a cheap alternative to building dams or filtration and drying systems. The report says 70 million to 90 million gallons of slurry is created nationwide each year.

In theory, solids settle to the bottom of pools inside sealed mine voids, and all the waste stays put, with little risk to groundwater below.

The industry defends the practice as safe. But critics say the earth continues to shift and crack long after mining has ended, whether through natural settling or activity such as nearby blasting. They say that lets slurry migrate, sometimes into drinking water supplies. Hundreds of southern West Virginia residents are now suing coal companies, claiming slurry poisoned their wells and made them sick.

WVU's report says federal documents and other literature provide reason to believe injection "does not always work as intended'' and can contaminate ground and surface water.

But there is virtually no useful monitoring data from the 12 active injection sites in West Virginia or dozens of others that were used for decades, the report says, and therefore no practical way to determine whether the slurry underground contains anything other than the 237 legally permissible chemicals.

Nor is there currently an effective way to trace the movement of slurry once it's injected into the worked-out mines where it hypothetically stays put. Current regulations fail to fully describe the process or address real-time monitoring, the report says, "so opportunities for early detection of quality assurance problems are not assured.''

If underground injection is to continue, the scientists conclude, "it deserves routine quality control.''

A legislative subcommittee is set to hear a presentation on the report Monday in Charleston and will hold the third of a series of hearings on slurry.

Kessler argued a temporary moratorium on new injection sites -- imposed by the DEP more than a year ago -- should be made permanent while legislators figure out how to provide public health officials more answers.

"If they need data and ongoing monitoring, we're going to legislatively require ongoing monitoring,'' he said. "I just am at a loss to understand how on earth it could be that difficult to run tests on known sites.''

It's unclear what the health department might recommend to develop more data. A spokeswoman for the DHHR said the agency will await direction from the Legislature.

DEP Secretary Randy Huffman said he had given the summaries and conclusions only a cursory reading but was open to whatever recommendations the scientists, health officials and legislators make.

The report does not appear to offer any evidence to "move me either way'' on outlawing underground injection, Huffman said, but he lacks the legal authority to do so anyway.

If legislators ban underground injection, he said, "then that's the law we'll enforce.''

In the meantime, Huffman said the temporary moratorium will remain in place and no new permits will be approved.

The report appears to identify "areas we need to shore up in our regulatory program, and we kind of expected that,'' Huffman said. But he added that he's uncertain how filling data gaps would help scientists draw any better conclusions about health risks.